Electronic systems and equipment such as computer systems, network interfaces, storage systems, and telecommunications equipment are commonly cooled using a pressurized under-floor plenum. Hot air exhausted by electrical equipment in a data center room is drawn into Computer-Room Air Conditioning (CRAC) units via powerful fans in the CRAC units. The CRAC fans cool the hot air by forcing the air through a liquid-to-air heat exchanger. Pressurized cooling air then enters a plenum beneath the data center floor. Cooled air is distributed to the equipment in the room by placing floor tiles with perforations in close proximity to the cool air inlet vents of the equipment.
Typically, during final stages of a data center upgrade or new construction, airflow through the perforated tiles is measured to plan for sufficient cooling to meet expected room equipment heat loads. Adjustments are made to the quantity and placement of the perforated tiles and CRAC blower speed is to set a desired air flow rate. Control of changes in flow rate is difficult to achieve once deployment is complete. However, unintentional changes to flow rate are common. Over time, flow rates generally decrease due to addition of cables and other obstructions in the plenum. Holes in the plenum are often created for cable routing and can cause drastic changes to initial tile flow rates by creating low-resistance bypass for the high-pressure cooling air. Therefore, attaining a planned airflow distribution in the data center is difficult due to the complex nature of airflow and pressure distribution in the plenum.
Air exits from the CRAC at a very high velocity. At a distance from the CRAC units, air velocities are low and uniform. The combination of conditions often results in a non-intuitive and undesirable airflow distribution through the perforated tiles. Airflow is low or negative, drawing air from the data center into the plenum, near the CRAC unit. In contrast, airflow is higher distal from the CRAC unit.